Light has a significant role in photography. Illumination is needed for generating an image onto a light sensitive sensor. The light travels via imaging optics typically through an adjustable aperture. The aperture can be made smaller, wherein the amount of light coming into a camera device is decreased. When the aperture is made larger, the amount of light coming into the camera device is increased. The imaging optics gather the light reflected from the imaged target and project the light to the sensor. If natural lighting is not high enough for photographs, the amount of light can be increased by additional lamps, flash lights, etc.
Optical zooming is a method where the optical magnification of the imaging optics is adjusted, due to which such targets, which are within a photographing region, are formed bigger or smaller in the final image on the image sensor depending on the direction of the zooming. The photographer can hence select the targets, which are wanted to be emphasized in the image, by zooming into them. When the target is in this way optically enlarged, the amount of light seen by individual pixels in the camera sensor becomes smaller, whereby the image becomes darker. This phenomenon, where use of camera optics for optical zooming reduces the amount of light falling on the image sensor when increasing optical magnification, is known in the art of photography.
For typical imaging optics the amount of the light can be estimated by the following equation:fact=fn×(M+1)
where fact corresponds to actual aperture value, fn to aperture setting in the imaging optics and M to zooming ratio. The bigger the zooming ratio (i.e. the closer to the image) is the less light is available. For example, if the zooming ratio is less than 1:10, the light does not substantially decrease. However photographing with zooming ratio of 1:1 and aperture value of 16 gives to the aperture the actual value of 32, which is two times greater than the aperture setting, whereby the light loss is two aperture values.
Some solutions are provided for overcoming the problem of light decrease in optical zooming. One possibility is to increase the analog signal gain, whereby the light in the analog signal domain will be amplified, but then because also the noise will be amplified, the signal-to-noise ratio will be typically decreased. Another possibility is to increase the image exposure time, whereby more photons may be gathered and thus a brighter image can be provided. However due to this solution, the image may be blurred if the exposure time becomes too long.
Some cameras have both optical and digital zooming capability. Digital zoom implements the zooming by magnifying the specific region in the digital image using digital image processing techniques after the image has been captured by the optical sensor. Because the image source (unzoomed image) has less information in that region than the final zoomed region needs to have, the image quality may suffer somewhat. Therefore the digital zooming is usually utilized only after the optical zooming has reached its maximum. However, in this case the light decrease in the image due to the optical zooming cannot be prevented, because digital zooming is applied to the optically zoomed image.
Therefore it seems that a solution that could better reserve illumination of the image, when optical zooming is used, is lacking from the related art.